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Homeoprotein SIX1 compromises anti-tumor immunity through TGF-β-mediated regulation of collagens

ABSTRACT: Purpose: The tumor microenvironment (TME), such as non-immune-infiltrated “cold” tumors, has been associated with immune suppression. However, the complex mechanisms regulating tumor immunogenicity have not been clearly elucidated. In this study, we investigated whether Transcription factor sine oculis homeobox 1 (SIX1) expression in the cancer cells regulated anti-tumor immunity by reshaping TME. Methods: The expression of SIX1 in human tumor tissues was analyzed based on TCGA data. Six1 knockout murine cell lines were generated to analyze the SIX1-associated tumor progression and anti-tumor immune response in tumor xenograft models. Immune cells and cytokines in TME were quantified by immunofluorescence, flow cytometry, quantitative reverse transcription-PCR, and ELISPOT assay. SIX1-associated differentially expressed genes were investigated in cancer cells and tissues with RNA-Seq. At the end, Correlation of SIX1 with TGFBR2 expression was assessed by Western blot and Dual-luciferase reporter assay. Results:SIX1 was highly upregulated in human tumor tissues, while rarely expressed in matched normal tissues. Deletion of the Six1 in cancer cells inhibited tumor growth, depending on adaptive immunity. Moreover, Six1 deficiency significantly enhanced CD8+ T cells infiltration, leading to eradication of poorly immunogenic tumors and maintaining a long-term protection from tumor re-challenge. Mechanistically, SIX1 as a transcription factor upregulated TGFBR2 expression, which induced collagen genes expression via the Smad2/3 phosphorylation, increased collagens deposition in TME and hampered CD8+ T cells infiltration. Conclusions: Six1 deletion in cancer cells improved tumor immunogenicity, leading to tumor destruction by enhancing anti-tumor immune responses. Our observations uncovered a crucial role of SIX1 on remodulating tumor immunogenicity and demonstrated a proof of concept for targeting SIX1 in cancer immunotherapy.

ORGANISM(S): Mus musculus

PROVIDER: GSE183580 | GEO | 2021/09/09

REPOSITORIES: GEO

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Project description:Immunotherapeutics represent highly promising agents with the potential to improve patient outcomes in a variety of cancer types. Unfortunately, single-agent immunotherapy has achieved limited clinical benefit to date in patients suffering from pancreatic ductal adenocarcinoma (PDAC). This may be due to the presence of a uniquely immunosuppressive tumor microenvironment (TME) present in PDACs, which creates a barrier to effective immune surveillance. Critical obstacles to immunotherapy in PDAC tumors include the dense desmoplastic stroma that acts as a barrier to T-cell infiltration and the high numbers of tumor-associated immunosuppressive cells. We have identified hyperactivated focal adhesion kinase (FAK) activity in neoplastic PDAC cells as a significant regulator of the fibrotic and immunosuppressive TME. We found that FAK activity was elevated in human PDAC tissues and correlates with high levels of fibrosis and poor CD8+ cytotoxic T-cell infiltration. Single-agent FAK inhibition (VS-4718) dramatically limited tumor progression, resulting in a doubling of survival in the p48-Cre/LSL-KrasG12D/p53Flox/+ (KPC) mouse model of human PDAC. This alteration in tumor progression was associated with dramatically reduced tumor fibrosis, decreased numbers of tumor-infiltrating immature myeloid cells and immunosuppressive macrophages. We postulated that these desirable effects of FAK inhibition on the TME might render PDAC tumors more sensitive to immunotherapy. Accordingly, we found that VS-4718 rendered the previously unresponsive KPC mouse model responsive to anti-PD1 and anti-CTLA4 antagonists leading to a nearly tripling of survival times. These data suggest that FAK inhibition increases immune surveillance by overcoming the fibrotic and immunosuppressive PDAC TME thus rendering tumors more responsive to immunotherapy. We treated KP orthotopic tumor-bearing mice with vehicle and FAK inhibitor (FAKi) for 14 days, then extracted total RNA from tumor tissues.

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Homeoprotein SIX1 compromises anti-tumor immunity through TGF-β-mediated regulation of collagens

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